Continuous casting process and apparatus



July 6, 1954 l. HARTER, JR

CONTINUOUS CASTING PROCESS AND APPARATUS Filed July 9, 1949 5Sheets-Sheet 1 INVENTOR F/ 1 [5/4/46 HARTE/Q JR.

' m. ATTORNEY y 6, 1954 i l. HARTER, JR 2,682,691 CONTINUOUS CASTINGPROCESS AND APPARATUS Filed July 9, 1949 5 Sheets-Sheet 2 lllllilll FIG.2

INVENTOR [5AA C HAR-TER, JR.

July 6, 1954 HARTER, JR

CONTINUOUS CASTING PROCESS AND APPARATUS Filed July 9, 1949 5Sheets-Sheet 3 INVENTOR ISAAC HARTER, JR.

BY V

ATTORNEY July 6, 1954 HARTER, JR 2,682,591

CONTINUOUS CASTING PROCESS AND APPARATUS Filed July 9, 1949 5Sheets-Sheet 4 XL *h Jl "w n M VVY "li l Al I 1 V 7 1 HLS TC 1 la l 0 lI m 1 A 1b L INVENTOR ISAAC HARTERJR. S BY 21? ATTORNEY y 6, 1954 l.HARTER, JR 2,682,691

I CONTINUOUS CASTING PROCESS AND APPARATUS Filed July 9, 1949 5Sheets-Sheet 5 x. l l ll a 15 4 1 K I Q 1 l I E cvcuc .2 WITHDRAWAL 1Ocommuoos a *WITHDRAWAL E 8 INCHES 0F RUN-OUT CA ST/A/GLENGTH 8 INVENTORISAAC HART/5R, JR.

ATTORN EY Patented July 6, 1954 TEES orricr.

CONTINUOUS CASTING PROCESS AND APPARATUS Isaac Harter, (in, Beaver, la.,assignor, by mesne assignments, to The Babcock & Wilcox Company, JerseyCity, N. 3., a corporation of New Jersey Applipa-tion July 9, 1949,Serial No. 103,901

for the continuous casting of high melting temperature metals, such asferrous metals and alloys, in semi-finished and/or finished products ofindeterminate length and various cross-sections.

In a related copending application of Harter et al., Serial No. 10,956,filed February 26, 1948, now Patent No. 2,590,311, dated March 25, 1952,it is disclosed that processes and apparatus have been in successfulcommercial use for years for the continuous casting of non-ferrousmetals, such as copper and aluminum, having relatively low fusiontemperatures and high thermal conductivities, but that such priorapparatus and processes have heretofore failed to result in a singleinstallation in commercial production for the continuous casting ofsteel/or alloy steel products.

The principal object of the present invention is the provision ofanimproved process of and apparatus for continuously casting metal insemi-finished or finished products of a commercially uniform andacceptable quality at a commercially economical rate of production,which process and apparatus are particularly characterized by themaintenance of more effective heat transfer conditions in the mold, theproprocess of and apparatus for continuous casting of the characterdescribed in which molten metal delivered at a substantially constantrate and temperature to an open-ended liquid-cooled stationary mold,subjected in the form of an embryo casting to alternating rates of heatabsorption while in the mold, then withdrawn from the mold as aself-sustainingcasting by a cyclic on and off or high and low speedmovement of the withdrawal mechanism. A further specific object of theinvention is the provision in a continuous casting process and apparatusof the character described or" a fluid cooled mold having an inner wallor liner formed of metal with a relatively high thermal conductivity andof a thickness providing a substantial heat storage capacity. A furtherspecific object of the invention is the provision of mechanism forautomatically controlling the rate of molten metal delivery to the moldin correlation with mechanism for automatically controlling a cyclicoperation of the structure throughout its length. I tinuous casting ofsteel, for example, steel of the- 2 casting withdrawal mechanism inresponse to time and/or molten metal level change.

While the process of the present invention can be used for thecontinuous casting of non-ferrous and ferrous metals and alloys, it isparticularly designed and especially useful for continuously castingferrous and other high melting point alloys to produce semi-finished andfinished castings, each of commercially acceptable quality and of asubstantially uniform metallurgical In the condesired composition isfirst melted in accordance with good steel making practice in ordelivered to a suitable heating and/or pouring vessel, such as a ladle.Ladle heating means insure that during the time of pouring, the metaltemperature will be within an optimum temperature range, which, Whilevarying with the metal composition, will normally be enough above theliquidus temperature of the metal to insure the desired fluidity of themetal. As much as possible of the slag present in the charge isseparately removed from or retained in the ladle. A tiltable ladlehaving. mechanism for controlling the rate of tilt is preferablyemployed to insure an approximately constant rate of pour of the moltenmetal. To minimize the amount of slag in the charge, the refractorylinings of the apparatus parts Which contact the molten metal areconstructed of the same or compatible ceramic composition, as disclosedin said copending Harter et al. application.

A special stationary casting mold assembly is employed which isconstructed to permit and maintain the desired high rate of heat absorption from the molten metal and embryo casting. The casting mold itselfis upright and open at both ends, and the delivery rate of molten metalto its upper-end and the rate or withdrawal of the casting from itslower end are coordinated to maintain in normal operation a varyinglevel of molten metal not exceeding a predetermined value within andbelow the upper end of the mold. The maximum molten metal level shouldnot be too close to the top of the mold due to possible metal oxidationbecause of exposure to the atmosphere. The stream of molten metaldelivered is also regulated by adjusting the position of tun dish, toenter the molten pool with a minimum or" splashing against the mold andof turbulence in the molten metal pool in the mold.

Complete elimination of oxygen from the mold atmosphere above the moltenmetal is highly desirable to prevent formation of metal oxides.

This is accomplished by the continuous introduction of an inert gas,preferably heavier than air and non-soluble in the metal, into the topof the mold to displace any lighter gas, such as air, therefrom and alsothe introduction of a substance which will consume any oxygen and/ordeleterious reactive gases that might remain in the mold. The combinedeffect produces a substantially oxygen-free atmosphere in the mold spaceimmediately above the molten metal level.

The present process of continuous casting of ferrous and other highmelting point alloys is particularly distinguished by the extremely highrate of heat transfer effected between the solidifying metal and themold cooling liquid. This is attained by employing an extremely highrate of mold cooling, as set forth in said copending Harter et al.application, in conjunction with an improved method of withdrawing thesoli fied casting from the mold assembly in a cyclic on and off or highand low speed movement.

As disclosed in said copending Harter et al. application, it has beenfound that for a commercially acceptable ferrous alloy casting process arate of heat transfer from the portions of the mold effective in theformation of the embryo casting is required which is at least severaltimes over the maximum cooling rate heretofore proposed in the prior artfor casting ferrous alloys. This extremely high cooling rate is attainedby the introduction of the cooling water into the stationary moldassembly in a manner and in quantities insuring the entry andmaintenance of a solid stream of cooling water throughout the moldcooling passage at a velocity having a calculated Reynolds number forhighly turbulent flow conditions, with pressure and flow so combinedthat far greater heat transfer rates than have been achieved in anyother known system are obtained.

In contrast to the substantially uniform rate of 'withdrawal of thecasting from the mold assembly disclosed in said copending Harter et a1.application, the present invention involves a con trolled cyclicoperation of the withdrawal mechanism, whereby the casting isalternately sub jected to periods of high rates of heat absorption whilestationary or substantially stationary in the mold and periods of lowerrate of heat absorption while moving downwardly in the mold.

The combination of a substantially constant molten metal delivery to thestationary mold with a cyclic on and off or high and low speed movementof the casting withdrawal mechanism results in a varying molten metallevel in the mold between predetermined limits, whereby the section ofthe mold liner within the molten metal level limits is alternately incontact with the metal and exposed to the mold atmosphere. During theexposure period this mold liner section continues to be cooled at thesame rate by the contacting cooling water, reducing the mold liner metaltemperature in this section substantially below its temperature when incontact with molten metal. As the molten metal level again rises, theheat storage capacity of the mold metal results in an initial chillingeffect on the contacting molten metal. If the mold liner is made as thinas structurally permissible, the heat storage eiTect would beinsignificant. In accordance with the present invention, the mold lineris preferably made of a metal having a relatively high thermalconductivity and of suflicient thickness to provide a substantial heatstorage capacity sufficient to give a substantial initial chilling efofthe wall within safe limits.

The amount of heat transfer by conduction per unit area between any twosurfaces in contact is dependent upon the closeness of contact, 1. e.the degree of conformity of the surfaces, the time in which the contactis maintained, and the temperature difference therebetween. Thistemperature difference in casting is primarily dependent upon thepouring temperature of the metal. The necessary higher pouringtemperature and inherently higher heat content per cubic inch of ferrousmetals and alloys make it more important in continuous casting thereofto maintain close intimacy of contact between the casting and mold inorder to obtain rapid solidification, and consequently increase theproblems of mold design, mold cooling, and method of operation, in orderto transfer the greater total amount of heat from the casting to thecooling liquid. Where freezing metal is continuously moved downwardly inthe mold, the degree of conformity of the molten metal will be highinitially, due to the inherent property of any liquid to conform to thewall of its container, but as the peripheral shell of frozen metal isformed and thickened, the degree of conformity decreases due tocontraction of the shell and deviations in the cross-sectionaldimensions of the subjaccnt portions of the mold. In view of thesubstantially greater contraction of ferrous alloys as compared to mostnon-ferrous metals, a partial gap heat barrier is almost instantaneouslyintroduced between an embryo ferrous casting and the mold wall. Whenthis gap develops, the rate of heat transfer to the mold decreases andthis lower rate of heat transfer continues until the internal reheatingof the casting and ferrostatic head causes the shell to expand to reducethe gap. In some cases it has been found that the expansion of thecasting reestablishes contact with the mold wall, but obviously thedegree of conformity will never be as high as the initial contactbetween the molten metal and mold wall. The cycle of shell freezing andcontraction, reheating and expansion continues during the downwardmovement in the meld. This breathing of the casting is repeated a numberof times, dependent upon the time required for reheating, the rate ofwithdrawal of the casting, and the axial length and cross-sectionalshape of the mold. After sufficient shell thickness is attained, furtherfreezing and contraction of the casting are simultaneous. The contacttime for any substantial amount of heat transfer between the movingcasting and mold will ordinarily be short.

The present process of cyclically withdrawing the casting is designed tosubstantially increase the time and number of heat transfer contacts perunit of mold length between the casting and mold, with a consequent gainin overall heat transfer efficiency of the mold assembly and im provedmetallurgical properties of the casting. For this purpose, in thepreferred normal operation the casting withdrawal mechanism is operatedwith an off and on cycle to first hold the casting stationary in themold during a varying period controlled by the rise in level of themolten metal in the mold to a predetermined extent. During this periodan extremely close contact is maintained between the molten metal andmold wall, causing the metal in the contacting outer ri-m portion tosolidify at a very rapid rate due to the high'rate of heat absorption ofthe mold and the stationary intimate contact of the metal. The controls,generally speaking, are set to maintain the oif period of the withdrawalmechanism, or dwell of the casting, for a time interval sufficient topermit the formation of an appreciably thick shell around the moltenmetal and a slight contraction of the shell away from the mold. Thistime interval 'iscoordinated with the rate of supply of molten metal tothe mold and when the rising level of molten metal during the dwell ofthe casting reaches a predetermined level, the withdrawal mechanismis-put into oper 'ation to permit the casting to move downwardly apredetermined increment of its length or period of time.

During the dwell period additional metal is poured into the mold at asubstantially constant rate. This additional metal is subjected to thehigh rate of heat absorption of the mold and a shell tapering upwardlyin thickness to a lacelike formation is formed thereon. On thesubsequent withdrawal movement of the casting, the lowermost portion ofthis shell stays joined to the shell on the metal present at the startof the dwell and tears away from the remaining Weaker section of theshell, the upper lacy portion of which, now unsupported by molten metal,tends to fall inwardly into the metal pool. The submerged intermediatesection appears to remain on the mold Wall, because sufiicientcontraction has not yet occurred, until the molten metal present fillsand heals the breach and is solidified during the withdrawal andsubsequent dwell period.

The decreased rate of heat absorption by the mold due to the gap heatbarrier permits the casting shell to be reheated by the enclosed core ofmolten metal and expand towards the mold wall under the ferrostatic headof molten metal. According to the present invention, this fluid pressureis increased at the end of each on period by rapidly decelerating thespeed of the withdrawal mechanism, causing the inertia of the core ofmolten metal to exert a hammer effect on the surrounding shell. Theadded expansion so given to the shell substantially reestablishes themold to shell contact and consequently a high rate of heat transferbetween the casting and mold. The expanded shell is thickened during thedwell of the casting and contracts by the time the withdrawal mechanismis again operated to repeat the cycle. As the casting proceedsdownwardly through the mold, each successive increment of withdrawal isless affected by the hammer effect until the increasing thickness andstrength of shell is sufficient to withstand the combined action of theferrostatic head and hammer effect, and this point determines theoptimum length of mold for a particular casting rate as aself-sustaining shell will now exist.

As the casting is withdrawn from the mold, it usually contains aV-shaped core of liquid metal. To solidify the core more rapidly andreduce shrinkage voids, the casting is preferably subjected to asubstantial liquid cooling effect close to the bottom of the mold Therate and amount of casting cooling in this zone is selected inaccordance with good metallurgical practice for the type of metal oralloy being cast to produce a completely solidified casting at a desiredtem perature. The casting can be subsequently reheated and recooledalternately to satisfy any particular metallurgical requirements. Fromthis core solidification zone, the casting concasting, thus insuring themetallurgical soundness of the casting product by eliminating voids.This hammer effect is also believed to have the further advantage ofoffsetting the necking of the casting which is believed to principallyoccur during the reheating cycles of the casting, i. e. when the shellhas contracted out of contact with the mold, in a continuous withdrawalprocess. The force causing the necking is the pull of the withdrawalmechanism when the friction in the mold is sufiicient to become aholding force.

It is a fact that the refractory lining of steel holding or heatingvessels is subject to erosion and/or build up, thus causing change ininternal contour. This changing contour causes difficulties in anyprogramed pouring control, especially for the nose tilting type ofpouring ladle. The required degree of precision of pouring from a ladleis advantageously less for an intermittent withdrawal of the castingthan for a continuous withdrawal. According to the present process,variations in the rate of molten metal supply to the mold are readilycompensated for by changes in the frequency of operation of thewithdrawal mechanism. The duration of the casting dwell period part ofthe cycle, 1. e. the time required for the incoming molten metal toreach a predetermined height in the mold after each withdrawal period,affords an effective check on the ladle control system. For example, ifthe duration of dwell period's continually decreases, it signifies thatthe incoming metal rate is too fast; if the duration of dwell'periodscontinually increase, the incoming metal rate is too slow. In eithercase, the ladle. tilt control can be manually adjusted in accordancewith the indications of dwell time duration to provide a substantiallyconstant average withdrawal rate from east to cast.

In spite of the best known methods and apparatus for the elimination ofor lightweight impurities, some slag enter a mold with the molten metal.Whenever cor able amount of slag is present in either a co tinuous orintermittent withdrawal casting process, the latter processadvantageously minimizes amount of slag contained in of entrapped on thesurface of the finished casting. "With the intermittent withdrawalprocess, the regulated changes in the molten metal levei encourages theentrapment of accumulated slag during each cycle of operation. On theother hand, with the continuous withdrawal, nominally constant moltenmetal level process, the slag generally accumulates during a much longertimed period per entrapment. The greater slag accumulation leads to anentrapped slag mass sufficient to form an appreciable heat barrier onthe surface of the casting which results in interior slow cooling andcreates casting defects. The various features of novelty whichcharacterize my invention are pointed out with particularity in theclaims annexed to and forming a part of this specification. For a betterunderstanding of the invention, its operating advantages and specificobjects attained by its use, reference should be had to the accompanyingdrawings and descriptive matter in which I have illustrated anddescribed a practical embodiment of my invention.

Of the drawings:

Fig. 1 is a partial side elevation of a continuous casting apparatusconstructed in accordance with the present invention, including adiagrammatic illustration of the metal pour rate control and the controlmeans for regulating the casting withdrawal mechanism;

Fig. 2 is an enlarged elevation view of the pouring means and asectional elevation view of the mold shown in Fig. 1;

Fig. 3 is a plan View, partly in section, showing the tun dish and theupper portion of the mold;

Fig. 4 is a wiring diagram showing the control circuit for thewithdrawal mechanism shown in Fig. 1;

Figs. 5, 6 and 7 are wiring diagrams showing other control circuits forregulating the withdrawal mechanism shown in Fig. 1; and

Fig. 8 is a graphical representation of the pounds of metal frozen in acontinuous casting mold operated in accordance with the presentinvention as compared with the pounds of metal frozen in the same moldunder substantially identical conditions, except for a substantiallyuniform casting withdrawal rate.

The embodiment of the present invention illustrated in the drawings issomewhat similar in general physical arrangement to the disclosure ofthe previously mentioned copending applications, now Patent No.2,590,311. In the following description, the term continuous casting isused to generically signify the formation of a cast metal product havinga length greater than that of its mold.

As shown in Fig. 1, the metal pouring means includes a vessel arrangedfor lip pouring, and a tun dish I! arranged to receive molten metal fromthe vessel and to deliver a substantially slag-free stream of metal to aselected position in the open upper end portion of a continuous castingmold assembly [2. The vessel [0 may be a melting furnace, or a holdingand pouring ladle arranged to be charged with molten metal as deliveredthereto by a transfer ladle. Advantageously the vessel 10 is heated, sothat the molten metal poured therefrom is delivered to the mold at asubstantially uniform temperature.

The vessel I8 is arranged for tilting movement about a transversehorizontal axis defined by trunnions 13 extending outwardly on oppositesides of an L-shaped frame 14 supporting the vessel. The trunnions aresupported in trunnion bearings is each of which is mounted on a pedestalI6 and arranged for sliding movement in a horizontal direction normal tothe axis of tilting movement. The transverse position of the vessel 10relative to the tun dish II is regulated by means of gear motors (notshown) connected to the adjusting screws IT. The tilting movement of thevessel is obtained by any suitable method, such as the operation of amotor driven drum hoist I8. The hoist is connected to the vessel ID by acable and a yoke 2! which is attached to the platform of the frame l4supporting the vessel.

The pour rate from a lip pour type of container, such as the vessel 10,is not uniform during a uniform angular rate of its tilting movement. Toattain pour rate uniformity the vessel must be tilted through a patternof a changing rate of angular movement. This preferred pattern oftilting movement can be determined experimentally or by calculation forany'specific internal shape of vessel. A tilting control system for apouring vessel utilizing a pattern of angular rate of movement for asubstantially uniform rate of pour is disclosed and claimed in thecopending application of T. W. Ratcliffe and S. 0. Evans, Ser. No.107,506, filed July 29, 1949, and is shown schematically in Fig. 1 ofthis application.

As shown, a pin cam 22 is driven at a uniform angular velocity by asynchronous motor 23 through an adjustable speed reducer (not shown).The cam contour is adjustable so that it can be correlated for anoptimum tilting rate of the pouring vessel II] to obtain the desireduniform metal pouring rate. The substantially uniform angular velocityof the cam shaft is converted to a selected varying angular movement ina manner hereinafter described, and an indication resulting from acomparison of such varying angular movement with the actual movement ofhoist l 8 is transmitted to a speed and direction control unit 24connected through an electrical cable 25 to a motor driven rheostat 26controlling the motor 21 of the hoist 18.

A continuous indication of such actual movement of hoist I8 is providedby a self-synchronous motion tra-nsmitter 39 driven by the drum andelectrically connected with a self-synchronous receiver 35. The actualrotation of the hoist, reproduced by the rotation of the shaft 32 of thereceiver 2-H, is fed to a differential comparator 33, and to anindicator arm 34. The comparator 33 is also fed by a shaft 35 rotated bymovement of cam 22 through a chain 36 riding on the cam contourthrough-the toothed pulleys El and 38, and the chain 29. An arm Allmounted on the shaft 35 indicates the movement of the shaft. The inputdriving gears of the gear box 33 are separately connected to the shafts32 and 35, and are arranged so that any difierential movement of theshafts effects rotation, in one direction or the other, of thedifierential output shaft t2 which in turn actuates the control unit 24.Thus the speed control device 26 will regulate the drum hoist motor inaccordance with the comparative movements of actual tilt rate and theoptimum pattern of the cam contour so as to maintain the actual tiltingmovement of the vessel 19 at an optimum metal pour rate.

The tun dish I l as shown particularly in Figs. 2 and 3, is disclosedand claimed in a copending application of I. Harter, Jr. et al., SerialNo. 2114, filed January 13, 1948, now Patent No. 2,571,033, datedOctober 9, 1951, and a division thereof, Serial No. 209,164, filedFebruary 2, 1951, and

is formed with a refractory lined rectangular.

cavity 44 divided by a transverse partition 45 having a port or ports 46in the lower end thereof for the passage of molten metal therethrough.Molten metal from the vessel It] enters the receiving chamber Eda of thetun dish cavity, with the entering stream of metal deflected through anangle of substantially by a submerged baffle 41. Any slag tends toaccumulate on the surface of the molten metal in the receiving chamberMa, and can be removed as it accumulates. The metal receiving chamber isprovided with a longitudinal dimension sufficient to permit a slightvariation in the delivery position of the entering molten stream withoutaltering the relative horizontal position of either the vessel It or thetun dish H or adversely influencing the slag separating effect of thebafiie 41. Molten metal passing through the port or ports 46 in thepartition 45 fills the discharge chamber 44b to the level of thedischarge li 48 and thence discharges into the open upper end of themold assembly l2.

Advantageously the tun dish i is mounted for a plurality of adjustments,so as to insure the delivery of molten metal into a preferred loca--tion in the mold. To insure a desirable fluidity of the molten metalpassing through the tun dish, a suitable fuel burner 43 is installed inthe top of the discharge chamber Mb. The gaseous products of the fuelburned in the chamber discharge through the molten metal discharge lipabove the molten meta-1 level maintainedv therein and thereby tend tomaintain the fluidity of the metal passing through the V-notch of thepouring lip. The tun dish is provided with trunnions 5c supported intrunnion bearings 5| carried on a base plate 52. The plate 52 issupported upon a plate member 59 which is pivotally supported at oneend, as at 53, with the plate 52 also mounted for horizontal movementson the plate member 59. The horizontal movements of the plate 52 and tundish ll relative to the member 59 are obtained by an angular movementabout a vertically arranged pin 54 affixed to the member 59 and atransverse movement movements are obtained "through the screwcranks 55and 55 respectively. In addition, the

tun dish is arranged for tilting motion about the trunnions 5G- with thetilted position of the tun dish adjusted by the screw crank 51 and arm58 shown in Figs; 1, 2, and 3. The adjustments in the positioning ofthetu'n dish are intended to permit the directing of the flow of themolten metal stream so that it will enter the mold at a preferredlocation.

The mold assembly !2 is described in considerable detail in the i-larteret al. application, Serial No. 10,956 and is shown in Figs. 2 and 3-. Asdisclosed and claimed therein, a stationary mold wall or molding tube 55isformed from brass, copper, or other suitable material selected with athermal conductivity and wall thickness suificient to attain asatisfactory heat fiow therethrough. The molding tube is open at bothends and is vertically elongated to provide a confining wall surface forthe formation of an embryo casting therein. The molding tube 60 may beof one piece or segmental construction, and is exterior-1y cooled by ahigh velocity confined stream of cooling water. To attain a satisfactorycommercial metal casting rate, the cooling water velocity must be suchas to insure highly turbulent flow along the exterior surface of themolding tube. As disclosed and claimed in the I. Harter, Jr. et al.application Serial No. 44,654, now abandoned, the tube 68 and itssurrounding cooling water passageway 6| are advantageously formed withan oval cross-section shape, where oval is defined as a figureby-symmetrically formed about perpendicularly intersecting major andminor axes. A typical mold cross-sectionand its relationship ,to the tundish H is shown inFig. 2.

The upper open end. of the molding tube 60 is supported in a. top plate90, whereby thetube is free to expand axially therefrom. The plate 90forms the top wall of an annularchamber shifting the plate: 52Lrelativeto the pin .54. These 9!, which is supplied with a flow of cooling waterthrough a plurality of inlet pipes 92. A metallic skirt 93' ofcorresponding cross-sectional shape surrounds the molding tube 60 todefine the cooling water fiow passageway 6i and'to confine the highvelocity stream of cooling water against the surface of the tubesubstantially throughout its length. The upper end portion of the skirt93 fits into a corresponding recess in a surrounding sleeve 94 extendinginto the chamber 9|, and defining a discharge Weir from the chamber 9|.The weir section of the sleeve 9 3 is shaped to form an anti-cavitationentrance nozzle to the passageway iii and to substantially uniformlyaccelerate and distribute the fiow of cooling water in its contact withthe exterior surface of the molding tube.

As indicated in Fig. 3, the tun dish and oval mold are relativelyarranged-so that the stream of molten metal will enter the open upperend of the molding tube in a trajectory in a vertical plane containingthemajor axis of the oval mold internal cross-section and impinge uponthe molten metal therein at or slightly beyond the intersection of themold minor axis. The resulting surface eddy currents cause any slag orferric oxides which may be floating on the surface of the molten metalto collect in the quiescent area behind the point of impingement of thede-- livered' stream and adjacent to the end of the mold nearer the tundish.

.In starting a casting operation, the usual sectional dummy is insertedin the mold with its upper end positioned at the expected minimum liquidlevel of molten metal therein and with. its lower end engaged by thecasting withdrawal mechanism, which, as shown in Fig. 1, consists ofvertically spaced pairs of pinch rolls H driven through suitable gearingby a variable speed electric motor in. The initially poured. metalfreezes around. a projection on the dummy end to form the connection forefiecting the casting movement.

The main feature of the present invention is the controlled cyclicmulti-change operation of the casting withdrawal mechanism whereby themolten metal and embryo casting are subjected to periods of high ratesof heat absorption while stationary or substantially stationary in themold and periods of lower rates of heat absorption while movingdownwardly in the mold, i. e. the withdrawal mechanism is operated incycles with each cycle comprising a dwell period and a run period. Ascompared to the heat absorption rate in such a mold with a continuoussupply of molten metal and uniform rate of withdrawal of the casting,the present operation of the withdrawal mechanism to include a dwellperiod in which the casting is stationary or substantially stationaryrelative to the confining wall of the mold produces a substantiallyhigher rate of heat absorption due to. the extremely close contactmaintained between the molten or partly frozen metal and mold.- wall,particularly in the initial freezing zone, and secondly, due totheheatstorage property of the molding tube in conjunction with avarying molten metal level in the mold. This varying molten metal levelis attained by the continuous substantially uniform delivery of moltenmetal to the stationary mold throughout each cycle. The level dropsduring the run period of the casting and rises during the dwell periodbetween predetermined limits, whereby a longitudinal section of themolding tube is alternately exposed to the mold atmosphere and coveredby molten metal. With the tube formed of a high thermal conductivitymetal, the continuous cooling action of the contacting cooling waterresults in the rapid lowering of the wall temperature in this section toa value approaching the cooling water temperature. The subsequentcontact of molten metal with this relatively cold molding tube wallsection produces a shock cooling efiect on the contacting metaldepending upon the heat storage capacity of the tube.

In accordance with the present invention, this shock cooling effect ismade substantial by forming the molding tube 60 of metal having arelatively high thermal conductivity and of a wall thickness sufiicientto provide a substantial chilling effect on the molten or partlysolidified metal in addition to the normal heat absorption by the -moldcooling water. The maximum molding tube wall thickness is limited onlyby the necessity of keeping the maximum metal temperature of the tubewithin safe temperature limits during operation. For example, a moldingtube of copper of approximately one-half inch thickness would besatisfactory for casting steel in accordance with the present process.

In carrying out this cyclic operation, the casting withdrawal mechanismcan be regulated in response to measurements of time, indication ofchanges in the molten metal level within the mold, or by a combinationof time measurement and level indication. With a selected castingaverage withdrawal rate and a substantially uniform rate of pour, theextent of molten metal level change is determined by the duration of therun and dwell periods.

The position of the molten metal level within a casting mold can bedetermined by the use of any suitable mechanical or electrical levelindicating means, such as, for example, the radiation type of moltenmetal level indicator disclosed in a copending application of T. W.Ratclifie et al., Serial No. 107,506, filed July 29, 194:9, now U. S.Patent 2,586,713. Such an indicator utilizes the difierence in radiationpenetration through a casting mold with and without the intervention ofthe molten metal level within the mold. As disclosed and claimed in saidcopending application of T. W. Ratcliife et al., the radiation type ofmolten metal level control is used in combination with a pattern controlof a tilting ladle to maintain a constant molten metal level in acasting mold by regulation of a continuous withdrawal rate. Thus, thelevel control is utilized as a vernier regulation to compensate for anynon-uniformity of molten metal pour rate to the mold. Suchnon-uniformity in pour rate can occur by reason of changes in theinternal dimensions of the pouring vessel due to erosion or build up ofits lining in contact with molten steel.

As shown schematically in Figs. 1, 2 and 3, a penetrating radiationmolten metal level indicator, constructed in accordance with said T. W.Ratcliife et a1. copending application, is arranged in the presentcyclic type of casting withdrawal control circuit to control the upperlimit of the molten metal level variation, and effect the start of therun period of the cycle. A source of penetrating radiation, such as anX-ray tube, is provided within a shielded container 62, with a stream ofpenetrating rays therefrom directed through a shielded conduit 63 acrossthe rear portion of the mold at the selected level for maximum moltenmetal level in the molding tube. At

the opposite side of the mold an ionization cham ber 54 receives anypenetrating radiation passing through the mold. An electrical meansmeasures the conductivity of the ionization chamber 64, so that apredetermined change in the conductivity thereof will indicate thepresence of molten metal at the level of the stream of penetrating rayspassing through the mold. As shown in Fig. 2, the transverse dimensionof the stream of penetrating rays passing through the mold is limited sothat a relatively small change in the molten metal level Will cause ameasurably large variation in the conductivity of the ionization chamber64. Changes in the conductivity of the ionization chamber aretransmitted electrically through the leads 65 to an amplifying circuit(not shown) and thence to a relay PR in a control box 66. The relay isconnected into an electrical control circuit regulating the controller88 of the pinch roll drive motor 10. The motor in is of the variablespeed type, with its speed of rotation regulated by any of the customaryelectric control systems.

In the apparatus shown in Fig. l, the penetrating radiation levelcontrol is utilized to limit the maximum rise of molten metal level inthe mold by initiating the operation of the pinch roll motor to withdrawthe casting from the mold at a rate in excess of the molten metal inputrate. The fall in molten metal level continues during a predeterminedperiod of time as regulated by an adjustable timer 72. At the end of aselected time period the pinch roll motor is stopped, or its speedreduced to permit the molten metal level to rise in the mold. When themolten metal level within the mold again occludes the penetrationradiation stream of the level control, the described withdrawal cycle isrepeated.

The control circuit for regulating the described cycle of pinch rollmotor operation is illustrated in Fig. 4, Where control circuit power isobtained through the lines L. The customary manual switch S is providedin the power line L so that the control system may be disconnected whennot in use. The contacts XH are closed by the penetrating radiationrelay when the molten metal reaches its highest level position in thecasting mold. This energizes the relay l closing the contacts la and lbstarting the timer clock cc and energizing the relay 2. With the contactla closed the pinch roll motor relay PR is energized, starting the pinchroll motor through the controller 68. In energizing relay PR, thecontacts PR2 and PR3 are closed. The contacts PR2 and PR3 are arrangedin parallel relationship with contacts in. and lb respectively so thatas the molten metal level falls in the mold with a resultant opening ofthe contacts XH the pinch roll motor relay will remain energized and thecasting withdrawal will continue. When the desired time has elapsed, asregulated by adjustment of the timer element TC, contacts TMC open todeenergize relay 2 and close contact 2a. With the contact 221 closed,the pinch roll motor relay PR will stop the motor '10 and open thecontacts PR2 and PR3. The resistance R! in the feed line to relay PRwill limit the load through the shunt line, including the contact 2a,until the contacts PR2 open.

The described off and on operation of the withdrawal mechanism ispreferably carried out with a dwell period of greater duration than therun period for maximum production capacity. With the described high rateof heat absorption in effect during the dwell period of the cycle, the

initial freezing of the molten metal to form the embryo casting,particularly when casting ferrous alloys, causes the metal to contractand move out of contact with the confining wall of the mold. With theformation of this air gap barrier, there would no longer be anyadvantage, in continuing the dwell period, and as the molten metal levelwill then have reached approximately the desired level, the controls areset to start the pinch rolls for the run period.

In one illustrative example of the described oif and on operation of thecasting withdrawal mechanism, molten steel of a common mild carbonanalysis was delivered to the upper end of an oval mold having interiormajor and minor axis dimensions of 9% and 4%; inches respectively. Themolten metal pour rate was equivalent to an average casting productionrate of approximately 39 inches per minute of cast product, ofapproximately this cross-section. During the cyclic intermittentwithdrawal of the casting as described, the off or dwell period averaged8.2 seconds and the on or run period averaged 11.6 seconds, with amolten metal level change of 5.2 inches during each operating cycle ofthe casting withdrawal mechanism.

The described off and on operation of the pinch rolls may be modified incertain instances to use a slow speed operation of the p nch rollsinstead of bringing the rolls to a complete stop, during the off ordwell period of the cycle. For such modified operation, the timercontrol '12 would be set to maintain a predetermined high speed ofwithdrawal above the rate of delivery of molten metal for a definiteperiod and then to actuate the motor speed control device to operate thepinch rolls at a speed producing a casting movement substantially belowthe rate of delivery of molten metal. With the resultant rise in metallevel, the level control mechanism, will subse-' quently operate torestore the speed control to its high speed operation and repeat thecycle.

The pinch roll and drive gear mechanism are of such construction thatwhen the drive motor is stopped or its speed suddenly reduced at the endof each on or run period, the withdrawal speed of the casting will berapidly decelerated, causing the core of molten metal in the upper endof the casting to exert the described hammer effect on the surroundingembryo shell. The rapid deceleration can be increased by any suitablemeans, such as for example by the operation of a brake l lmounted on theshaft connecting the drive motor 10 and the pinch rolls H. The brake canbe of any suitable mechanical or electrical type actuated incoordination with the stoppage or change in speed of the motor it.

Alternately, as shown in Fig. 5, the casting withdrawal cycle may beregulated by a pair of level controls of the penetrating radiation typedescribed. In such an arrangement the level controls are spacedlongitudinally of the mold and electrically connected to the control box66 to cause the pinch rolls H to start to operate at a high speed whenthe molten metal level reaches the position of the upper level control.This high speed casting withdrawal continues until the molten metallevel falls to the position of the lower level control. At this positionthe pinch rolls are stopped or caused to withdraw the casting at a lowrate, causing a rising molten metal level in the mold. As shown in thewiring diagram of Fig. 5 the contact XH is closed when the molten metallevel rises to its upper position in the mold and occludes the radiationof the level control. Closing contact XI-I energizes the relay PR. tostart the pinch roll motor 10, and to close the contact PR2. As themolten metal level drops the contacts Xl-I will open, but the pinchrolls will continue to operate until the molten metal level falls to thelevel of the lower level controller. At this lower level, the change inpenetration radiation measured in the ionization chamber will close thecontacts XL, deenergizing the relay PR to stop the pinch roll motor.

When the molten metal pour rate can be maintained uniform, it ispossible to regulate the cyclic withdrawal of the casting by means oftimers alone. Under such circumstances the high speed casting withdrawalperiod can be regulated by a timer, while the stopped or low speedwithdrawal period can be regulated by a second timer, such timers beingof the type of the timer 12 indicated in Fig. l, and arranged in thecontrol circuit of the motor it. The control circuit of pinch rollcontrol of this type is shown in Fig. 6, wherein the circuit isenergized, by closing the manual switch S at the beginning of the dwellperiod, e. the period of rising molten metal level. This energizes thedwell timer 12 and the relay 2, to open the contact 2a and 2b. The pinchroll relay PR is not energized during this timed period and the pinchroll motor will not run. At the end of the timed dwell period determinedby adjustment of TC the contacts TMC open to deenergize relay 2 andclose contacts 20. and 2b. Closing the contact 22) starts the pinch rollmotor while 2a starts the run timer i2, and energizes relay I. With therelay 1 energized contact la is opened to reset the dwell timer circuit'12, so that the cycle may be repeated when the run timed period haselapsed as determined by the adjustment of TC, and the contacts TMC haveopened to deenergize relay I. p

With a uniform molten metal pour rate, the casting withdrawal mechanismcan also be regulatedby the use of a molten metal level indicator of thepenetrtaing radiation type positioned at the lower end of the desiredmolten metal level range within the mold, in conjunction with a timerfor regulating the time during which the withdrawal mechanism is stoppedor operated at a low speed, thus permitting the molten metal level torise within the mold, and then starting the high speed operation of thepinch rolls which is subsequently terminated by the level control. Thecontrol circuit for this mode or operation is shown in Fig. 7. Thiscircuit is substantially the same as that shown in Fig. 4, exceptactuation of the penetrating radiation control at the lower limit ofmolten metal level in the mold stops the operation of the pinch rollmotor. This permits the molten metal level to rise during a timed periodas determined by the adjustment of the timer element TC. At the end ofthe timed dwell period the deenergization of relay 2 closes the contact211 to cause a fall in molten metal level through operation of the relayPR, and the pinch roll motor.

As a safety measure when the duration of the run or dwell periods isgoverned by a timer of the character described, it is usually desirableto supplement the timer control by a molten metal level control, such asof the penetrating radiation type described, to avoid any change in themolten metal level beyond a predetermined limit established by the levelindicating device. The use of the level controller as a safety limitswitch is illustrated in Figs. 4, 6 and 7.

In Fig. 4 the contacts XL and LLS are opened when the lower molten metallevel is reached, stopping the pinch rolls until the molten metal risesbeyond the control'level when the contacts are again closed and thenormal cycle is continued. In Fig. 6 both a high and low level safetycontroller are used, with the high level controller closing the contactXl-I and opening contact HLS to operate the pinch rolls to lower themolten metal level within the mold. The low level controller opens thecontacts XL and LLS to stop the pinch roll motor to raise the moltenmetal level in the mold. In Fig. 7, the upper level controller is shownas a safety control, where a rising molten metal level reaching thelevel of the controller causes contacts XH and I-ILS to close, operatingthe pinch rolls to lower the molten metal level within the mold.

As the embryo casting leaves the mold in its cyclic downward movement,the casting passes through a core solidification zone in which it issubjected to a supplementary cooling eiiect to reduce the castingtemperature at least to a value at which the casting will be completelysolidified. Various cooling means can be employed for this purpose, butI prefer to use cooling water sprays in direct contact with the casting.As shown in Fig. 2, spray nozzles 15 are peripherally spaced on theinner side of a horizontally arranged manifold 16 encircling thecasting. The lower end of the molding tube 60 carries a frusto-conicalmember 1'! enclosing the manifold 15 and arranged to deflect the coolingwater flowing downwardly through the passage 6| away from the casting.Beneath and within the periphery of the member 11, a verticallyelongated tubular shield 78 encloses the casting so as to furtherprotect the casting from the excessivc cooling eiiects of the moldcooling water. A gap SI is provided between the upper end of the shield78 and the member H for the escape of steam resulting from theevaporation of the water sprays contacting the casting. Ordinarily theamount of water sprayed against the casting will be only a smallfraction of the amount of cooling water passed through the moldpassageway 6!, and is completely evaporated on contact. However, theamount of spray cooling water used may be substantially increased,depending upon the composition of the metal being cast and the effect ofsuch rapid cooling on its metallurgical quality.

To insure peripherally uniform cooling of the casting in the mold andthe spray cooling zone,

it is desirable to provide a guide or guides above the pinch rolls H tomaintain the vertical alignment of the casting. A pair of stationaryguides 82, shown in Fig. l, are mounted within the shield 18. Theseguides may be water cooled and restrain any tendency for transversemovement of the hot casting which might cause the emerging casting tobear upon one side of the lower end portion of the molding tube 60.

In operation, molten metal is delivered to the upper end of the mold I2at a substantially uniform temperature and rate, and with the embryocasting withdrawn from the lower end of the mold in a controlled cycleof downward movement. With the described cyclic withdrawal of thecasting, the increased amount of heat extracted from the hot metalwithin the mold is illustrated in Fig. 8. The solid line indicates theprogressive freezing of steel in the mold under continuous withdrawalconditions while the dotted line indicates the progressive freezing ofsteel in the same mold with a cyclic off and on operation of the castingwithdrawal mechanism according to the present invention. The valuesindicated in Fig. 8 were obtained by molten metal run-out procedure,where an oxygen lance was used to burn a hole through the side wall ofthe casting at a position immediately below the lower end of the moldingtube 66 to permit the molten metal core to run out, and simultaneouslystopping the molten metal delivery to the upper end of the mold. Whenall of the casting variables are comparable, i. e. metal analysis,temperature of delivery, rate of delivery, and cooling fluid flow to themold are substantially equal, the weights of solidified metal in therun-out section of the casting would be equal, unless the castingwithdrawal method is changed. The increased metal freezing rate withinthe mold attained by the cyclic casting withdrawal system of the presentinvention is apparent by a comparison of the curves shown in Fig. 8.

While in accordance with the provisions of the statutes I haveillustrated and described herein the best forms of the invention nowknown to me, those skilled in the art will understand that changes maybe made in the form of the apparatus and method of manufacture disclosedwithout departing from the spirit of the invention covered by my claims,and that certain features of my invention may sometimes be used toadvantage without a corresponding use of other features.

What I claim:

1. The process of continuously casting molten ferrous metal in anopen-ended vertically elongated stationary mold liner made of highthermal conductivity metal and having a laterally confined space aroundsaid mold liner for the flow of a liquid coolant therethrough and acasting withdrawal mechanism spaced below said mold liner whichcomprises continuously supplying a stream of molten metal to said moldliner from a discharge point above the normal maximum molten metal leveltherein, maintaining a non-oxidizing atmosphere within said mold linerabove the molten metal level therein, circulating a liquid coolant at ahigh velocity through said space in heat absorbing contact with saidmold liner to form an embryo casting within said mold liner, discharginga cooling liquid against the casting on issuing from said mold liner,guiding and restraining said casting between said mold liner and saidwithdrawal mechanism, and cyclically varying the molten metal level insaid mold liner by starting said withdrawal mechanism when the moltenmetal level rises to a predetermined position within said mold liner,and stopping said withdawal mechanism after a predetermined downwardmovement of said casting.

2. Apparatus for continuously casting molten ferrous metal comprisingmeans forming an open-ended vertically elongated stationary mold linerof high thermal conductivity metal, means forming a laterally confinedspace around said mold liner for the high velocity flow of a liquidcoolant therethrough, means for circulating a liquid coolant throughsaid space in heat absorbing contact with said mold liner, means forsupplying a stream of molten metal to said mold liner from a dischargepoint above the normal maximum molten metal level therein, means formaintaining a non-oxidizing atmosphere within said mold liner above themolten metal level therein, a casting withdrawal mechanism spaced belowand in vertical alignment with said mold liner and arranged to engagethe castng discharged from said mold liner, spray means between thelower end of said mold liner and said withdrawal mechanism and arrangedto discharged a cooling liquid against the casting on issuing from saidmold liner, casting guide means positioned between the lower end of saidmold liner and said withdrawal mechanism, and means for cyclicallyvarying the molten metal level in said mold liner including means forstarting said withdrawal mechanism when the molten metal level rises toa predetermined position within said mold liner, and means operable tostop said withdrawal mechanism after a predetermined downward movementof said casting.

3. Apparatus for continuously casting molten ferrous metal according toclaim 2, wherein the means for starting the withdrawal mechanismcomprises molten metal level responsive means positioned externally ofthe mold liner and com nected to said withdrawal mechanism for startingsaid withdrawal mechanism in response to the presence of molten metal atan upper position within said mold liner.

4. Apparatus for continuously casting molten ferrous metal according toclaim 2, wherein said means operable to stop the withdrawal mechanismcomprises a timer arranged to start with the operation of saidwithdrawal mechanism and operatively connected to stop said withdrawalmechanism at the end of a predeter mined timed period.

5. Apparatus for continuously casting molten ferrous metal according toclaim 2, wherein the means for starting the withdrawal mechanismcomprises a timer arranged to start when the withdrawal mechanism stopsand operatively connected to start said withdrawal mechanism at the endof a predetermined timed period, and said means operable to stop thewithdrawal mechanism comprises a timer arranged to start with theoperation of said withdrawal mecha nism and operatively connected tostop said withdrawal mechanism at the end of a predetermined timedperiod.

6. In continuous casting apparatus for high melting temperature metals,the combination in cluding an upright elongated molding tube open atboth ends, means for cooling the exterior of said molding tube by heatexchange with a cooling fluid, means for delivering molten metal to theupper end of said molding tube at a substan tially uniform rate, awithdrawal mechanism spaced below and in alignment with said moldingtube arranged to engage the casting formed within said tube, a drive forsaid withdrawal mechanism, means for cyclically varying the molten metallevel in said molding tube comprising molten metal level responsivemeans externallyof the molten metal space and connected to saidwithdrawal mechanism for starting said withdrawal mechanism in responseto the presence of molten metal in an upper position within said moldingtube, a timer arranged to start with the operation of said withdrawalmechanism and operatively connected to stop said withdrawal mechanism atthe end of a predetermined timed period, and said molten metal levelresponsive means including means for continuing the operation of saidwithdrawal mechanism beyond the end of said timed period if the moltenmetal level in the molding tube is then not below a predetermined upperlevel position.

7. A continuous casting apparatus for high melting temperature metals,the combination ineluding an upright elongated molding tube open at bothends, means for cooling the exterior of said molding tube by heatexchange with a cooling fluid, means for delivering molten metal to theupper end of said molding tube at a substantially uniform rate, awithdrawal mechanism spaced below and in alignment with said moldingtube arranged to engage the casting formed within said tube, a drive forsaid withdrawal mechanism, means for cyclically varying the molten metallevel in said molding tube comprising molten metal level responsivemeans externally of the molten metal space and con nected to saidwithdrawal mechanism for starting said withdrawal mechanism in responseto the presence of molten metal at an upper position within said moldingtube, a timer arranged to start with the operation of said withdrawalmechanism and operatively connected to stop said withdrawal mechanism atthe end of a predetermined timed period, and separate molten metal levelresponsive means positioned above said first means and operativelyarranged to continue the operation of said withdrawal mechanism beyondthe end of said timed period if the molten metal level in the moldingtube is then not below the upper level position of said separate moltenmetal level responsive means.

8. Apparatus for casting metals comprising a thick-walled uprightmolding tube formed of a metal having a high thermal conductivity andopen at both ends, means for cooling the exterior surface of said tube,a pouring vessel arranged to deliver molten metal at a substantiallyuniform rate into the upper end of said tube for the formation of anembryo casting therein, a set of pinch rolls arranged to withdraw theembryo casting from the lower end of said tube, a motor arranged todrive said pinch rolls, means for cyclically changing the molten metallevel within said mold comprising means positioned externally of themolten metal space of said molding tube and operatively connected withsaid motor to cause operation of said rolls at a casting withdrawal ratein excess of said pouring rate when the molten metal rises to an upperlevel within said mold, and separate means positioned externally of themolten metal space of said molding tube and below said first means andopeartively connected with said motor to stop said motor when the moltenmetal level within said molding tube falls to a lower positioncorresponding to the level of said separate means.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,088,171 Pehrson Feb. 24, 1914 1,139,888 Mellen May 18, 19152,206,888 Greenidge July 9, 1940 2,246,907 Webster June 24, 19412,284,503 Williams May 26, 1942 2,284,703 Welblund et al June 2, 19422,284,704 Welblund et al June 2, 1942 2,290,083 Webster July 14, 19422,303,139 Roemer Nov. 24, 1942 2,323,128 Hare June 29, 1943 2,459,892Palmer et a1. Jan. 25, 1949 2,560,639 Giesler et al July 17, 1951FOREIGN PATENTS Number Country Date 598,385 Great Britain Feb. 17, 1948

